Fluorescence detection is an indispensable technique for the analysis of a variety of biological phenomena. During the past few decades, a number of small molecule fluorescent chemosensors have been developed for use in biological analyses, which typically are elaborately designed to selectively detect a target substance or phenomenon. (See (a) Geddes, C. D.; Lakowicz, J. R., Topics in Fluorescence Spectroscopy, Vol. 9; Springer: New York, 2005. (b) Geddes, C. D.; Lakowicz, J. R. Topics in Fluorescence Spectroscopy, Vol. 10; Springer: New York, 2005, the teachings of both are incorporated herein by reference).
Embryonic stem cells (ESCs) are derived from the inner cell mass (ICM) of blastocyst-stage embryos and have the ability to self-renew indefinitely. ESCs are pluripotent because they have the capacity to give rise to differentiated progeny representative of all three embryonic germ layers, as well as the extraembryonic tissues that support development. In mammals, the property of pluripotentiality is restricted to the oocyte, the zygote, early embryonic cells, primordial germ cells, and the stem cells of tumors derived from pluripotential cells (embryonal carcinomas).
ESCs can be characterized by high level expression of Oct-3/4 (also termed Oct-3 or Oct-4), a member of the POU transcription factors, and Nanog. A critical amount of Oct-3/4 and Nanog expression is required to sustain stem-cell pluripotency. When ES cells are induced to differentiate, Oct-3/4 and Nanog are down-regulated, which has proven to be essential for a proper and divergent developmental program. Each stage of ESC differentiation can be monitored by immunocytochemistry methods. The methods for probing mouse embryonic stem cell are generally diagnosed by cell surface antibody such as Nanog, Oct4 or GFP fluorescence protein. However, these protocols are limited mainly because of late stage of stem cell differentiation and selectivity.
Therefore, there is a need for a means by which the differentiation process can be monitored, which can reduce or eliminate one or more of the above-mentioned problems.